Current state-of-the-art defibrillators that are used for emergency resuscitation typically include a pair of hand-held paddle electrodes that are used to transfer a pulse of electrical energy to the body of a patient. As is known in the art, one of the first steps of using the paddle electrodes in an attempted resuscitation (or other therapeutic procedures such as cardioversion) involves coating the surface that will contact the body of the patient with an electrically conductive gel or other material. The paddle electrodes are then placed against the patient's body with the gel serving as a low-impedance interface and the electrodes being positioned so that a pulse of electrical current that passes between the electrodes travels through the patient's heart. Currently, one of two electrode placement arrangements is preferred. In the first arrangement, which is known as anterior/anterior placement, one paddle electrode is placed lateral to the upper sternum and below the right clavicle on the right-hand portion of the patient's chest and the second paddle is placed on the patient's lower left chest, usually below and lateral to the cardiac apex. In the second currently preferred electrode placement, which is known as anterior/posterior placement, one electrode is placed on the patient's chest over the precordium and the second electrode is placed on the patient's back behind the heart.
A patient requiring emergency resuscitation usually is unconscious. Since both hands of the operator must be utilized to hold the paddle electrodes properly and firmly in position and since the defibrillator operator must otherwise remain clear of the patient during the defibrillation procedure, paddle electrodes are not well suited for anterior/posterior use. Even in non-emergency usage such as cardioversion where the patient often is conscious or at least responsive to voice command, it is inconvenient to use paddle electrodes in the anterior/posterior positioning arrangement. Specifically, during such procedures, the patient usually is lying on his or her back to facilitate both the positioning of defibrillator electrodes and conventional ECG electrodes that are utilized in monitoring the patient's cardiac rhythm during the procedure.
Over the past several years, considerable effort has been expended to develop disposable defibrillator electrodes that can be used as an alternative to paddle-type electrodes. This effort has resulted in disposable defibrillation electrodes that exhibit electrical characteristics comparable to paddle electrodes. These disposable defibrillation electrodes are relatively flexible, exhibit a relatively low profile, and include an adhesive peripheral region that allows the electrode to be secured to the patient's skin. Thus, disposable defibrillation electrodes are better suited for anterior/posterior electrode positioning than are paddle-type electrodes. Moreover, disposable defibrillation electrodes sometimes are preferred regardless of whether anterior/anterior or anterior/posterior electrode placement is to be used. For example, it often is desirable to maintain a defibrillator in a ready or standby condition when a patient who has been resuscitated outside a clinical environment is being moved to a hospital or other care facility, during intensive clinical care of a cardiac patient, and during the performance of various medical procedures. In this situations, disposable defibrillation electrodes can be properly positioned and attached to the patient's skin before an emergency arises, thereby facilitating rapid defibrillation should the procedure subsequently be needed.
Since the alternative use of paddle electrodes or disposable defibrillation electrodes is dictated by the situation at hand and by the personal preference of the medical practitioner, attempts have been made to configure or adopt defibrillators for accommodation of both paddle electrodes and disposable defibrillation electrodes. In the simplest arrangement, the defibrillator includes one or more connectors to which the selected type of electrodes can be electrically interconnected with the defibrillator. One disadvantage of this arrangement is that the paddle electrodes may not be connected to the defibrillator when an emergency arises in which the paddle electrodes are needed. In addition, it has become common practice to mount controls and indicators on the paddle electrodes to facilitate both selection of the defibrillation energy level and administration of the defibrillation energy without assistance of a second person and with minimum attention being pad to controls and indicators that are mounted on the defibrillator unit itself. In such arrangements, selectively connecting the desired electrodes to the defibrillator results in the need for placing a second set of controls and indicators in the defibrillator that duplicates those controls and indicators that are located on the paddle electrodes. This requirement not only results in additional device complexity, but also means that medical personnel that are trained in the use of the device must master two separate control procedures.
One prior art proposal that eliminates a portion of the disadvantages associated with selectively connecting the paddle electrodes or disposable defibrillation electrodes to a defibrillator consists of an accessory unit that is temporarily or permanently mounted to the cabinet of the defibrillator. This prior art arrangement includes a cable having one end adapted for electrical interconnection with a pair of disposable defibrillation electrodes. The second end of the cable is electrically connected to conductive plates that are mounted on the upper surface of the accessory unit. When a defibrillator equipped with the accessory unit is to be used with disposable defibrillation electrodes, the electrode snaps (36, 38) are installed to the accessory unit cable and attached to the patient's body at the desired locations. The pulse of defibrillation energy is then administered when the operator places the paddle electrodes on the two conductive plates of the accessor unit and operates the defibrillator controls in the same manner as is utilized when the paddle electrodes are used in contact with the patent's body.
Although the above-mentioned type of accessory unit allows continued availability of the paddle electrodes and does not require separate indicators and controls when disposable defibrillation electrodes are employed, certain other disadvantages and drawbacks are encountered. For example, a defibrillator using such an accessory must include a relatively flat and rigid surface to which the accessory can be mounted for ready access by the handheld paddles without obstructing various defibrillator controls and indicators or obstructing access to the device for service or battery replacement. Further, this type of prior art arrangement for using disposable defibrillation electrodes offers little or no response time improvement relative to conventional use of the paddle electrodes. Specifically, in order to administer a defibrillation pulse, the operator must grasp the handles of the paddle electrodes, remove the electrodes from their stowage position, place the electrodes on the conductive plates of the accessory unit, and then sequence the defibrillator controls to administer the defibrillation pulse.
U.S. Pat. No. 4,628,935, issued to Jones et al. on Dec. 16, 1986, and assigned to the assignee of this invention discloses a defibrillator arrangement which overcomes the above-discussed prior art disadvantages. In that arrangement, an accessory cassette is provided that is adapted for interconnection of the defibrillator with either disposable defibrillation electrodes of the above-discussed type or with internal electrodes of the type used to effect defibrillation during surgical procedures in which the heart is exposed. In the arrangement of Jones et al., the upper surface of the defibrillator includes a slot for receiving a downwardly extending tabular portion of the accessory cassette. Electrically conductive contact regions positioned on the downwardly extending tabular portion of the cassette establish the necessary circuit paths between the defibrillator and cassette. In addition, when the cassette is installed to the defibrillator, nonconductive portions of the downwardly extending tabular region pass into and separate electrical contacts within the defibrillator to appropriately modify the defibrillator electrical circuitry for operation with the cassette.
Although the arrangement disclosed by Jones et al. overcomes the above-discussed disadvantages of the prior art, a need exists for alternative arrangements. For example, the arrangement of Jones et al. is not well suited for retrofit applications in which it is desirable to adapt previously manufactured defibrillators that are equipped only with paddle electrodes for use with disposable defibrillation electrodes. In addition, the arrangement of Jones et al. satisfies a design constraint that is not present in all situations. In particular, the arrangement disclosed by Jones et al. allows the defibrillator to be readily adapted for provision of various features. For example, one commercial embodiment of the arrangement of the Jones et al. patent includes not only a cassette for adapting the defibrillator for use with disposable defibrillation electrodes, but also includes an optional cassette for adapting the device to operation as an external cardiac pacemaker. Numerous design situations arise in which the plug-in feature versatility of the Jones et al. apparatus is not required. It is those situations and the previously mentioned retrofit situations, to which the present invention is directed.